[OnionSoup] Remove typemapping of (FetchAPIRequest, WebServiceWorkerRequest)

This CL removes typemapping of
(blink.mojom.FetchAPIRequest, blink::WebServiceWorkerRequest), instead,
we use blink::mojom::FetchAPIRequest struct directly.

This reduces lots of usages of blink::WebServiceWorkerRequest, now its
only usage is to carry the request data of a fetch event dispatched
towards a service worker, from //content across the boundary into Blink.

BUG=789854

Change-Id: Ife644a71941ea8db9f7798d414d49f2a0c61cf61
Reviewed-on: https://chromium-review.googlesource.com/c/1322360
Commit-Queue: Leon Han <leon.han@intel.com>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610047}
22 files changed